An intriguing if less-than-full investigation, “The Blackout Experiments” looks at several repeat participants in an activity many would pay not to experience: an “immersive horror” show individually tailored to play on their deepest fears and insecurities, utilizing tactics that can encompass established torture techniques. (Hence the legal waiver they’re required to sign first.) The creators of these Blackout events cooperated with Rich Fox’s documentary to an extent but, for the sake of maintaining their mystique, declined to be interviewed, so a number of basic questions go under answered here. What “Experiments” does expose is the always puzzling if not-uncommon need for some people to invite fear and pain — within limits. This sole documentary in Sundance’s 2016 Midnight section packs just enough curiosity value to court minor theatrical and slightly wider home-format sales.

Blackout’s creators, Josh Randall and Kristjan Thor, apparently started creating these “shows” 12 years ago, though that’s not in the film. Nor are any details about their working methods, how the project has evolved over that time, or even how much it costs to sign on. What we do glean is that potential participants have to fill out a questionnaire asking numerous personal details, and then, if accepted, are given the address of a secret, oft-changing location just the night before their appointment. Upon arriving, they’re typically yanked inside an empty commercial space temporarily “blacked out” with plastic tarp, where they are blindfolded or gagged, and generally manhandled. The disorienting experience is different for all (and different each time for repeaters), but can encompass forced nudity, verbal abuse, restraints, brief suffocation, even waterboarding.

For many, this is probably just one more thrill-junkie extreme to check off the bucket list. (Blackout has held its events irregularly in New York and Los Angeles for some time now, accruing a cult following and reputation.) But for the half-dozen or so regulars that Fox focuses on, it provides a confrontation with the “dark side” that can be variably traumatizing, therapeutic and addictive — or all the above at once. It’s often hard to tell whether they’re facing their fears or masochistically reveling in them. (Nor are they sure about that themselves.) Though these folks are actually paying money to see how far they can “test what (they’re) capable of enduring,” psychologically and otherwise, one young man is furious when he thinks they’ve gone too far with him. He protests “This isn’t a haunt, this is abuse,” scoffing that it’s just a glorified form of S&M.

On the other hand, several others are even more upset when they’re given an “ultimatum” and made to promise that this is their last Blackout — the idea being, presumably, that they have already faced their limits and can now go forward with their lives as healthier, happier beings. It would be interesting to have a mental-health expert or two weigh in on that (one participant’s wife is indeed a therapist who does not approve of his Blackout obsession), but “Experiments” doesn’t step outside its narrow purview enough for such outside analysis. The result is interesting enough, but feels a bit overextended at feature length considering the limited insight afforded.

Holding many of his own interviews in near-complete blackness, and allowed some access to the clients’ Blackout trips (plus surveillance-type footage shot by the organizers during each “show”), Fox does his best to reproduce a credibly nerve-jangling experience for the viewer, though it’s just not very scary to watch as a secondhand observer. Pic is well assembled, particularly in the editorial department, and boasts an original score (commingled with the Blackout events’ own sound designs) whose creepy atmospherics and sonic jolts would work very well in a regular fictive horror film.